Re: [RFC PATCH 1/8] mm/damon/core: safely validate src on damon_commit_ctx()

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [High] Validation step incorrectly tests the existing context (`dst`) instead of the new parameters (`src`), completely neutralizing the patch's safety guarantees.
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commit 4ac81fdba8a8c8576fad127fdd4347015f4dac51
Author: SJ Park <sj@kernel.org>

mm/damon/core: safely validate src on damon_commit_ctx()

This commit updates damon_commit_ctx() to validate parameters safely by
applying them to a test context before applying them to the running context.
If the test context validation succeeds, the real update proceeds.

> diff --git a/mm/damon/core.c b/mm/damon/core.c
> index 5febe58a07028..5ca176eb27e1d 100644
> --- a/mm/damon/core.c
> +++ b/mm/damon/core.c

[ ... ]

> @@ -1635,6 +1622,52 @@ int damon_commit_ctx(struct damon_ctx *dst, struct damon_ctx *src)

[ ... ]

> +int damon_commit_ctx(struct damon_ctx *dst, struct damon_ctx *src)
> +{
> +	struct damon_ctx *test_ctx;
> +	int err;
> +
> +	test_ctx = damon_new_test_ctx(dst);
> +	if (!test_ctx)
> +		return -ENOMEM;
> +	err = __damon_commit_ctx(test_ctx, dst);

[Severity: High]
Does this code incorrectly validate the existing context instead of the new
parameters?

test_ctx is initialized as a clone of dst via damon_new_test_ctx(dst). If
__damon_commit_ctx() applies dst to test_ctx again, it avoids testing the
new parameters in src entirely.

If src contains invalid parameters (like a non-power-of-two min_region_sz),
it will bypass this check. When the unvalidated src is subsequently applied
to the running context:

    err = __damon_commit_ctx(dst, src);
    
it can fail partway through. This leaves dst->maybe_corrupted = true and
causes the running kdamond monitoring thread to terminate unexpectedly.

Should the validation step be checking src instead?

    err = __damon_commit_ctx(test_ctx, src);

> +	if (err)
> +		goto out;
> +	err = __damon_commit_ctx(dst, src);
> +out:
> +	damon_destroy_ctx(test_ctx);
> +	return err;
> +}

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Sashiko AI review · https://sashiko.dev/#/patchset/20260701144815.113325-1-sj@kernel.org?part=1